The South Korean stem cell pioneer Hwang Woo-Suk publicly apologised today after an official investigation found two female scientists in his laboratory donated their own eggs for his research.

Professor Hwang had previously denied eggs from his researchers were used, insisting they all came from outside donors.

But he was forced to admit today that he had been untruthful after a health ministry ethical investigation concluded that two of his junior scientists at Seoul National University had contributed eggs.

The ministry said the donations were not technically in violation of South Korean ethical guidelines because they were made voluntarily.

But under commonly observed international guidelines, scientists are advised to be cautious when using for research human subjects who are in a dependent relationship with them, a precaution against exploitation.

At a news conference, a contrite Prof Hwang admitted he had made a mistake by being untruthful after the allegations were first made by the scientific journal Nature in May 2004.

Prof Hwang said: "I regret that if I had told the truth then I wouldn't have caused such concerns to the public now. I have learned a painful lesson that I should conduct research in a calm and cautious manner by living up to a global standard."

He said he had previously told his staff not to use their own eggs and that he only found out about the issue after being contacted by Nature. He said he spoke to the women and later denied the allegations because one of them had asked him to keep the matter private. However he added that "the responsibility for all disputes and controversy lies on me".

Appearing downcast and solemn, Prof Hwang told reporters that "to atone to the public" he would resign as head of the world stem cell hub he launched last month in Seoul along with other international researchers.

The foundation aimed to establish a centre seeking treatments for now-incurable diseases and had announced plans to open cloning centres in London and San Francisco. But Prof Hwang's US collaborators, including University of Pittsburgh researcher Gerald Schatten, dropped out of the project following the allegations of unethical egg collection.

Today Prof Hwang said he would continue his research.

A trained veterinarian, Prof Hwang is a national hero in South Korea and has gained international renown for his breakthroughs, including cloning the world's first human embryos and extracting stem cells from them.

Earlier this year, he unveiled the world's first cloned dog, Snuppy the Puppy, a feat recently praised in Time magazine's annual survey of the world's most remarkable inventions.

The health ministry also confirmed that Prof Hwang was recently told that a doctor who had earlier been collecting eggs for his research paid some women for their eggs.

Prof Hwang said today he had asked the doctor about the source of the eggs and was told not to worry about it and continue his work.

The payments to egg donors ended in 2003 and were not illegal at the time. This year, a new South Korean law took effect banning commercial trading of human eggs.